Many processes are known in the art for forming a composite wood element product from a composite mat assembly of resin coated wood elements. For example, steam and microwave energy have been used in conjunction with a variety of press assemblies to heat the mat assembly to about the cure temperature of the resin and compress the mat assembly to a desired final dimension. However, the designs of the prior press assemblies are relatively inefficient.
Steam injection heating sources unduly limit the size of the composite wood element products that can be formed. The heat carried by the steam must naturally conduct into the central portion of the product to raise the product to the cure temperature. Natural flow through a wood product is limited to certain thicknesses for certain products. Products over 5 inches thick can be very difficult to evenly heat. Further, steam injection presses are fixed in length and are not continuous in operation, limiting the length of the product. Thus, steam injection heating does not allow the production of relatively larger wood element products. By limiting the size of product that can be produced from a given press assembly the press assemblies ultimate utility is limited.
Traditional microwave heating systems have helped solve some of the heat transfer problems. However, the design of these microwave heating systems creates another problem. More specifically, current designs have no balance between the time at which a mat assembly reaches the cure temperature and the time in which the same mat assembly reaches a fully compressed state. The result is either a mat assembly where the resin is cured before reaching final compression or a failure to bring the mat to the optimal temperature at all. The percentage of the energy that can be delivered by preheat is thus limited. In both cases an undesirable result is attained.
Press assemblies using microwave applicators directing microwave energy into the sides of the mat assemblies have been developed in an attempt to address these issues. However, the side application systems have their limits as well. Placing a microwave waveguide assembly within a press limits the type of press assemblies that can be used. More specifically, many press assemblies are designed such that it is physically impossible to place a waveguide assembly at the side of the press. Consequently, press assemblies that may otherwise be highly desirable for other reasons may be prevented from being used by their design.
Examples of various microwave curing systems are U.S. Pat. No. 5,228,947 issued Jul. 20, 1993, U.S. Pat. No. 6,290,809 B1, issued Sep. 18, 2001, U.S. Pat. No. 6,242,726 B1, issued Jun. 5, 2001, U.S. Pat. No. 4,020,311, issued Apr. 26, 1977, U.S. Pat. No. 4,456,498, issued Jun. 26, 1984 and U.S. Pat. No. 6,176,951 B1, issued Jan. 23, 2001. All of which are incorporated herein by reference.